Skin, the body's largest organ, is composed of multiple layers. The outer layer, epidermis, is divided into several sublayers; the outermost layer is termed stratum corneum epidermidis. The stratum corneum is generally a non-innervated cell layer consisting of mainly large, dead cells that lack nuclei. Beneath the epidermis, lies the dermis skin layer, which is tightly connected to the epidermis.
A major structural component of the skin is collagen, a fibrous protein, which contributes to skin strength and elasticity. As such, collagen formation and remodeling lead to changes in mechanical properties of the skin such as texture and resilience. Typically, collagen plays an important role in the regeneration of epidermal tissue in wounded skin. Collagen is produced during the wound healing process, thus increasing the tensile strength of a wound.
Collagen contraction, or thermal shrinkage of collagen, occurs by the dissociation of heat-sensitive bonds of the collagen molecule. Thermal denaturing of collagen results in a tightening effect of the skin. In contrast, age-related degradation of collagen leads to sagging of the skin and the formation of wrinkles. Many wrinkles appear on exposed areas of the skin, e.g., the face, the neck and the forearms. These visible effects of aging of the skin are disturbing to some individuals, and therefore methods for rejuvenation of maturing or damaged skin are of interest.
U.S. Pat. No. 6,461,354 to Olsen et al. describes systems and methods for selectively applying electrical energy to a target location on an external body surface, such as for skin tissue removal and/or collagen shrinkage in the epidermis or dermis, e.g., the removal of pigmentations, vascular lesions (e.g., leg veins), scars, tattoos, etc., and for other surgical procedures on the skin, such as tissue rejuvenation, cosmetic surgery, wrinkle removal, hair removal and/or transplant procedures. The described system and methods apply high frequency (RF) electrical energy to one or more electrode terminals adjacent an external body surface, such as the outer surface of the skin, to remove and/or modify the structure of tissue structures within the skin. Depending on the specific cosmetic procedure, the described system and methods may be used to: (1) volumetrically remove tissue or hair (i.e., ablate or effect molecular dissociation of the tissue structure); (2) separate a tissue layer from an underlying tissue layer so that the tissue layer can be removed; (3) shrink or contract collagen connective tissue; and/or (4) coagulate blood vessels underlying the surface of the skin.
U.S. Pat. No. 6,381,498 to Knowlton describes a method and apparatus that applies radiant energy through the skin to underlying collagen tissue, and is described as not substantially modifying melanocytes and other epithelial cells in the epidermis. A membrane is adapted to receive an electrolytic solution and become inflated to substantially conform to a contacting exterior surface of the membrane to a skin layer. The membrane includes a cooling lumen for receiving cooling fluid. One or more thermal electrodes positioned in the membrane transfers thermal energy to the electrolytic solution. The electrolytic solution and cooling fluid is described as creating a reverse thermal gradient from the skin surface to the underlying collagen tissue. A thermal power source is coupled to the thermal electrodes, and a source of electrolytic solution is coupled to the membrane.
US 2006/0036300 to Kreindel describes a method of lipolysis. The method comprises deforming a region of skin so that the region of skin protrudes from surrounding skin. One or more radio frequency (RF) electrodes are positioned on the protruding region of skin so as to generate an electrical current through adipose tissue in the protruding region of skin when a voltage is applied to the electrode or electrodes. A voltage is then applied to the electrode or electrodes so as to deliver sufficient RF energy to the protruding region of skin to damage subcutaneous adipose tissue. The described method may be used, for example, to achieve a reduction in body weight, cellulite reduction, loose skin reduction, wrinkle treatment, body surface tightening, skin tightening, and collagen remodeling.
U.S. Pat. No. 6,684,107 to Binder describes a system for reducing wrinkles on human skin that utilizes an electrode to conduct a microcurrent through the surface of the wrinkle into the underlying dermal layer. The electrode is moved in multiple passes along the length of the wrinkle, with the electrode in contact with the surface of the wrinkle while generating a periodically repeating microcurrent having a peak amplitude in the range of 10-40 microamps, a peak current density in the range of 10-50 microamps/cm.sup.2, and a frequency in the range of 5-15 Hz. The electrode device is described as self-contained in a battery-containing, cordless case from which a contact electrode protrudes. A hand-engaging second electrode on the surface of the case completes a conductive path through the user's body.
U.S. Pat. No. 6,148,232 to Avrahami describes a device for ablating the stratum corneum epidermidis of a subject, including a plurality of electrodes, which are applied to the subject's skin at respective points. A power source applies electrical energy between two or more of the plurality of electrodes, in order to cause ablation of the stratum corneum primarily in an area intermediate the respective points.
U.S. Pat. No. 6,611,706 to Avrahami describes a device for facilitating transdermal passage of a substance through skin on the body of a subject. The device preferably includes an electrode and a control unit. In a preferred embodiment, the control unit is adapted to drive the electrode to apply to the skin a current capable of ablating stratum corneum epidermidis of the skin, so as to facilitate transdermal passage of the substance. The control unit detects generation of at least one spark responsive to application of the current, and modifies a parameter of the current responsive to detecting the generation of the at least one spark.
U.S. Pat. No. 6,708,060 to Avrahami describes a device for treating skin on the body of a subject. The device includes a plurality of electrodes, which are adapted to be placed in contact with the skin and then moved across the skin while maintaining electrical contact with the skin. The device additionally includes a power source, which is adapted to apply a current between two or more of the plurality of electrodes at the same time as the electrodes are being moved across the skin.
Reliant Technologies (California, US) distributes the Fraxel family of cosmetic products, which includes three fractional lasers that produce two non-ablative treatments and one ablative treatment.
The following patent and patent applications may be of interest:
US 2005/0003518 to Avrahami et al.
US 2005/0119605 to Sohn
US 2005/0187497 to Nguyen
US 2006/0089688 to Panescu
US 2007/0270732 to Levine
US 2007/0287949 to Levine et al.
US 2007/0292445 to Levine
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